Pressurized entrained flow high-temperature black liquor gasification (PEHT-BLG) is a novel technique to recover the inorganic chemicals and available energy in black liquor originating from kraft pulping. One of the key parts in the PEHT-BLG process is the spray atomizer where the viscous black liquor is disintegrated into a spray of fine droplets into the hot gasifier. In this study a high-speed photography system was used in order to visualize the spray formation of black liquor and syrup/water mixtures at elevated ambient pressures based on a conventional coaxially convergent gas-assisted atomizer. The main conclusion is that the breakup and atomization of black liquor by a gas-assisted atomizer is similar to that of a syrup/water mixture with similar physical properties. The observed difference in sphericity between black liquor and syrup/water may be explained by rapid cooling of the black liquor by the cool nitrogen gas at the nozzle exit, resulting in a sudden decrease in viscosity and possible skinning of the black liquor. Furthermore, it was found that an increased ambient pressure appeared to contract the spray to a more dense cloud of droplets compared to the corresponding atmospheric case. © 2009 by Begell House, Inc.